The company announced the signing of a share sale agreement with Custom Mining late yesterday.

The deal includes a $65 million cash payment; $200 million in Macarthur shares at a volume weighted average share price over the previous 30 days; and up to another $10 million in Macarthur shares to be issued on March 31 of next year to a value cap of $9.00 per share.

Each share transfer is subject to conditions being met.

In addition to Custom's 70% stake in the Middlemount project, Macarthur will also gain a farm-in agreement for up to a 70% stake in the Dingo West project.

Macarthur Coal CEO Nicole Hollows said the deal was in line with the company's aims to be a leading independent Australian coal company.

"This opportunity represents a strong fit with Macarthur Coal's existing operations by expanding our market share of LV PCI coal and diversifying our product range with semi-hard coking coal in the future," Hollows said.

The Middlemount project has a JORC measured resource of 30.6 million tonnes, an indicated resource of 37.8Mt and an inferred resource of 31.7Mt - totalling 100.1Mt.

It is found 6km southwest of the Middlemount township in Central Queensland, about 280km from the Dalrymple Bay Coal Terminal and 390km from the port of Gladstone.

Bulk sample opencut mining activities have commenced at the site and it is anticipated 70% of the mine's production will be high-quality coking coal with the remainder a low volatile PCI coal.

Hong Kong-based commodities trading house Noble Group holds the remaining 30% of the project and holds an option to acquire an additional 20% stake in the project for $100 million.

In a second transaction with Noble Group, Macarthur has entered into a heads of agreement to sell a 19.61% interest in its subsidiary, Monto Coal 2, for a total consideration of $48.5 million.

Macarthur holds a 51% stake in the Monto Coal Joint Venture.